1. Field of the Invention
This invention relates generally to fabrication of substrates for multi-chip modules and other integrated circuit modules, and, more particularly, to fabrication of a substrate for an integrated circuit module by molding material around semiconductor chips, except for chip surfaces containing contact pads.
2. Description of the Related Art
Conventional high density interconnect (HDI) processes often use cavities formed into a substrate base for the placement of chips so that the top surfaces of the chips are essentially planar with the surface of the substrate. The substrate is generally a ceramic or a composite structure. The conventional HDI technique for fabricating cavities in the substrate is to mechanically machine or mill out the cavity material with a computer-controlled diamond tooled bit. This time consuming process does not always provide the desired chip cavity depth and can result in cracks which render the substrate unusable.
In the conventional HDI process, chips are placed into cavities on multiple drops of die attach adhesive for mechanical, thermal, and electrical mounting. Chips placed with this process often are displaced during further processing because there are non-uniform surface tension forces at the chip-to-die attach adhesive inter-face. This displacement reduces precision in chip location, and further processing steps are required to adapt each electrical interconnection to the chip misalignment.
Eichelberger, U.S. Pat. No. 5,091,769, issued Feb. 25, 1992, describes an integrated circuit package formed by placing integrated circuit chips backside down on a substrate, encapsulating the faces and sides of the chips, fabricating vias and interconnections through the encapsulant to the contact pads for testing and burn in procedures, and removing the encapsulant after testing. When chips of differing thicknesses are used in a single multi-chip module (MCM), their pads are not situated in a common plane, so this method requires either that some of the chips be thinned or that the vias be of varying depths. Additionally, this technique involves a step of mechanical grinding for planarizing the surface and the use of an encapsulant material which is removed after testing.